Motor vehicle door reinforcement tube and a process for manufacturing the reinforcement tube

ABSTRACT

A reinforcement tube having high strength, toughness and resilience for use as an absorption element in a motor vehicle door, the reinforcement tube having a cross-section in which a first dimension of the cross-section is greater than a second dimension of the cross-section, the second dimension being perpendicular to the first dimension.

This is a divisional application of Ser. No. 07/604,058, filed on Oct.26, 1990, now U.S. Pat. No. 5,093,990.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a motor vehicle door reinforcement tube havinghigh strength, toughness and resilience for use as an impact absorptionelement for a motor vehicle door, in particular the door of a passengercar.

2. Background Information

These door reinforcement tubes are used as braces in motor vehicle doorsto absorb the impact energy in lateral collisions and convert the impactenergy into mechanical work, with the intent being to ensure theintegrity of the door structure. For such a door reinforcement tube toperform this safety function, the tube must possess the followingcharacteristics, for example:

    ______________________________________                                        Tensile strength                                                                              Rm       min.    1100 N/mm2                                   Limit of elasticity                                                                           Rt       min     800 N/mm2                                    Elongation at failure                                                                         A5       min.    8%                                           ______________________________________                                    

or a W-150 energy absorption of at least 1900 Joule, as a function ofthe profile dimensions.

These minimum requirements can be higher or lower, as specified by theautomobile manufacturer.

The energy absorption is tested by deflecting a door reinforcement tube150 mm in a 3-point bending test. The force applied is recorded over thedeflection and the surface area below the curve is determined. Thisintegral then gives the desired energy absorption characteristic.

In automobile construction, in addition to many special developments,two basic problems are constantly being addressed: the reduction of thevehicle weight, and an increase in the passive safety provided to theseated passengers.

One proposed solution for these problems is disclosed in German PatentNo. 37 28 476, in which, through the use of a particular steel alloy,the tensile strength and limit of elasticity values of a doorreinforcement tube are increased compared to the prior art. Onedisadvantage of this proposal is that the reinforcing effect is achievedonly by the addition of relatively expensive elements such as nickel andmolybdenum.

According to another proposal, German Patent No. 36 06 024, a protectiveelement made of light alloy is used to reinforce the vehicle door atboth ends of the vehicle door. This nearly square reinforcement elementis not intended for narrow vehicle doors with a low insertion depth, andis designed with thick walls to compensate for low strength values,which means that the advantage of the lower specific weight of the lightalloy is largely eliminated. Moreover, this reinforcement element is notvery adaptable to different vehicle doors, as different doors mayrequire different dimensions. Also, for each reinforcement element thatis needed, a new extrusion die needs to be created, which extrusion dieis expensive to make.

OBJECT OF THE INVENTION

The object of the present invention is to provide a tubular steelreinforcement element which uses an economical steel alloy and whichreinforcement element can be manufactured with the conventionalproduction equipment which is used for the manufacturing of round tubes.

SUMMARY OF THE INVENTION

The tubular steel reinforcement element of this invention has therequired mechanical characteristics, is lightweight, and is alsosuitable for installation even in narrow vehicle doors.

This object is achieved by forming the reinforcement tube so that atleast a portion of the tube has a non-circular cross-section such thatthe longer axis is at least 20% longer than the shorter axis which isperpendicular to the longer axis. Advantageous refinements and a processfor the manufacture of such a profile are also disclosed.

The proposed tubular steel reinforcement element utilizes the knowledgethat the energy absorption ability is a function of, among other things,the magnitude of the section modulus of the structural part. Since thesection modulus is a function only of the structural configuration, thetubular steel profile according to the invention has a segment extendinglongitudinally with a curved exterior contour and a cross-section whichis not circular, whose longer axis is at least 20% longer than theshorter axis perpendicular to it. So that the higher section modulus,which is in the longer axis, can be fully utilized when thereinforcement tube is installed in the vehicle door, the longer axis ofthe steel profile cross-section is parallel to the direction of theimpact. The deformed cross-section is preferably elliptical or oval, andcan extend over the entire length of the steel reinforcement element oronly over a central area.

The shaping of the circular cross-section into an elliptical or ovalcross-section is done by cold pressing a primary tube which has a roundcross-section after the tube is first hardened. The material in thedeformed segment is thereby cold work hardened, whereby the cold workhardening also contributes to increasing the energy absorptioncapability of the tube. The degree of shape deformation should be atleast 15%. The original tube with a circular cross-section can be eithera seamless or welded tube, whereby conventional tube productionprocesses such as hot rolling or welding (e.g. HF process) can be usedin the tube formation. The required strength and limit of elasticity aregenerally achieved by means of an annealing with a subsequent quenchingin water, oil, or air. Alternatively, a material can be used which makespossible the hardening of the steel tube directly from the rolling heat,without a separate and subsequent heat treatment. The increase of theresilience by utilizing a higher section modulus with a simultaneouscold work hardening of the deformed segment can be used to reduce thewall thickness and/or the diameter of the steel tube accordingly,thereby saving weight. Alternatively, the increase can also be used toprovide the tubular, hardened steel reinforcement element with corrosionprotection by means of a subsequent hot dip galvanizing, without runningthe risk that the mechanical values, which are reduced by the temperingeffect of the galvanizing, will drop below the specified minimum values.

In addition to an elliptical or oval cross-section, other non-circularcross sections can also be used (e.g. a rectangular cross-section). Butall cross sections having corners are more difficult to manufacture thanoval or elliptical cross-sections. The manufacture of the ellipticalcross-section is theoretically simple, since all that is necessary is toplace the original circular tube under a press and to shape segments ofthe tube, or the entire tube to the desired cross-section by means offlat plates or with appropriately shaped dies. Alternatively, steelprofiles having an oval cross-section can also be manufactured directlyby a hot rolling process. The transport of such oval reinforcementelements in the finishing shop is difficult, however, since the tubescannot simply be rolled from one place to another. The straightening ofsuch tubes, primarily when they have been hardened, while theoreticallypossible, is very difficult to perform. The straightening machines whichare required are also very complex and expensive to design and procure,and can only be used for specific diameters. For major dimensionalchanges, the set of straightening rollers must always be completelyreplaced. For this reason, this alternative process of shaping the steelprofiles having an oval cross-section is no longer used.

The effect of an increase of the resilience can only be utilized if thesegment having a non-circular cross-section extends over a certainlength in proportion to the total length. Therefore, the minimum lengthof this segment should be 25% of the total length. Likewise, it isnecessary for the ratio of the major axis to the minor axis of thecross-section to exceed a certain specified value, so that thedeformation from the circular shape is significant. Therefore, thisratio should be at least 1.20, and for an elliptical cross-section, avalue of 1.25 is preferred.

It is also proposed that the segment be formed so that the cross-sectionin the center of the steel reinforcement element has the highest ratioof major to minor axis, and that this ratio decreases to 1 toward bothends of the tube (the ratio of 1 corresponding to a circular shape).This would be appropriate for a segment extending over the entire lengthof the tubular steel reinforcement element as well, since the centralarea makes the largest contribution to the level of the energyabsorption ability.

According to known mathematical formulas for the relationship betweenthe deflection line and the section modulus, a stronger tube can beobtained by one refinement of the invention which proposes areinforcement for the central region. This reinforcement consists of acylindrical metal sleeve, which, before the cold pressing into anelliptical or oval cross-section, is pushed onto or into the tubularsteel profile as an outer or inner tube, respectively. To fix theposition of this reinforcing sleeve, the sleeve can be provided with anadhesive, for example, or the sleeve can be connected to the tubularsteel profile by welding or soldering. Another type of fixing ispossible if a slit sleeve is used, the dimensions of which are selectedso that a clamping action is produced. A clamping action can also beachieved with a closed sleeve, if care is taken that, in the case of aninner sleeve, it has a thinner wall, and in the case of an outer sleeve,it has a thicker wall than the steel profile.

Another alternative to the addition of a reinforcing sleeve, in anotherrefinement of the invention, is that the segment with the oval orelliptical cross-section has a wall which is thicker than the wall ofthe adjacent regions. This has the advantage that the transition fromthe thickened region to the adjacent regions is continuous, therebycreating no attachment problems. Such a thickening over a specifiedlength, regardless of whether the thickening extends radially outward orinward, or is uniformly distributed both outward and inward, can beproduced by means of various manufacturing methods. One of thepossibilities, for example, is drawing with a tapered mandrel (GermanPatent No. 30 21 482) or chipless shaping such as pressing, rolling orhammering (German Patent No. 36 10 481). The advantage of integralthickening compared to the sleeves pushed over or inserted into the tubeis that the reinforcement can be directed more toward the outside ormore toward the inside, as appropriate, with regard to the desiredexterior dimensions, the weight of the component and the size of theload-bearing cross-section. Alternatively, instead of using either asleeve, or an increased wall portion, both a sleeve and a thickened wallportion could be used conjunctively.

To reduce the risk of buckling of the tubular steel reinforcementelement in case of impact, and/or to displace the occurrence of bucklinguntil after the specified 150 mm deflection has been reached, theinvention also proposes that the interior of the central segment befilled with a medium which has a low specific gravity. Material mixturesfor such reinforcement foams are disclosed, for example, in U.S. Pat.No. 4,861,097. Alternatively, metal foams or wood can also be used.

The advantage of the proposed tubular steel reinforcement element isthat by increasing the section modulus and by means of the thorough coldwork hardening of the shaped segment when it is deformed into an oval orelliptical cross-section, the weight of the reinforcement element issimply and economically reduced. Moreover, the invention can use asimply and economically manufactured round tube from existing productionlines as the original tube used for the making of the tube of thepresent invention.

One aspect of the invention resides broadly in a door for a motorvehicle, the door comprising: a framework having an inner side, an outerside and a peripheral edge; an inner panel secured to the inner side ofthe framework; an outer panel secured to the outer side of theframework; releasable locking apparatus disposed on the framework forretaining the door in a closed position; sealing device secured to theperipheral edge; the sealing device being for providing a seal betweenthe door and the motor vehicle when the door is in its closed position;hinges disposed on the framework for hingedly attaching the door to themotor vehicle for movement of the door away from the motor vehicle to anopen position and towards the motor vehicle to a closed position; atleast one reinforcement element secured to at least one of theframework, the outer panel and the inner panel; the at least onereinforcement element being disposed for providing protection againstcollisions to the door of the motor vehicle; the at least onereinforcement element having: a first end, a second end, and a centerportion disposed between the first end and the second end; a length; across-sectional area defining a first axis and a second axissubstantially perpendicular to the first axis; and a dimension of thecross-sectional area taken along the first axis of at least a portion ofthe reinforcement tube having a length greater than a length of adimension of the cross-sectional area taken along the second axis of theat least a portion of the reinforcement tube.

Another aspect of the invention resides broadly in a tubular steelreinforcement element for a motor vehicle door, the tubular steelreinforcement element having: a first end, a second end, and a centralportion disposed between the first end and the second end; a length; across-sectional area, the cross-sectional area defining a first axis anda second axis substantially perpendicular to the first axis; and adimension of the cross-sectional area taken along the first axis of atleast a portion of the reinforcement tube having a length greater than alength of a dimension of the cross-sectional area taken along the secondaxis of the at least a portion of the reinforcement tube.

Yet another aspect of the invention resides broadly in a process for themanufacture of a tubular reinforcement element for a motor vehicle door,the reinforcement element having high strength, toughness andresilience, and the process comprising the steps of: hardening a steeltube, the steel tube having a cross-sectional area, and thecross-sectional area defining a first axis and a second axissubstantially perpendicular to the first axis; and compressing at leasta portion of the tube so that a dimension of the cross-section takenalong the first axis of the at least a portion of the tube is longerthan a dimension of the cross-section taken along the second axis of theat least a portion of the tube.

The tubular steel reinforcement element is explained in greater detailwith reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an automobile having a door reinforced with a tubularreinforcement element.

FIG. 2 shows a longitudinal section through a tubular steelreinforcement element according to the invention, with threecorresponding cross sections along lines A--A, B--B and C--C.

FIG. 2A shows a cross-sectional view through the tube of FIG. 2 takenalong line A--A.

FIG. 2B shows a cross-sectional view through the tube of FIG. 2 takenalong line B--B.

FIG. 2C shows a cross-sectional view through the tube of FIG. 2 takenalong line C--C.

FIG. 3 shows a graph of the energy absorption capability of a tubularsteel reinforcement element according to the invention compared to astandard tube.

FIG. 4 shows a longitudinal section through a centrally-reinforcedreinforcement tube with a corresponding cross-section along line D--D.

FIG. 4A shows a cross-sectional view through the tube of FIG. 4 takenalong line D--D.

FIG. 5 shows a longitudinal section through an integratedcentrally-reinforced reinforcement tube with a correspondingcross-section along line E--E.

FIG. 5A shows a cross-sectional view through the tube of FIG. 5 takenalong line E--E.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts an automobile with doors 1', 3' which have reinforcementtubes 2' secured inside the doors to provide reinforcement to the doorfor protection upon a lateral collision by another vehicle.

FIG. 2 shows portions of a longitudinal cross-section of the tubularsteel reinforcement element according to the invention, and locateddirectly beneath it, FIGS. 2A, 2B, and 2C, show three correspondingcross sections of the tubular steel reinforcement element I along linesA--A, B--B and C--C of FIG. 2. The original tube illustrated here by wayof example has the following dimensions after hardening: outsidediameter 31.8 mm (2), wall thickness 2.3 mm (3), total length 864 mm(4).

For purposes of illustration, in this tubular steel reinforcementelement 1, a segment 6 in the central area, extending over a length 5 of250 mm, has been cold-formed with an oval cross-section B--B. Here, thelength 7 of major axis 20 of this oval cross-section B--B is, forexample, 37.0 mm and the length 8 of minor axis 21 is 25.4 mm. The ratioof the major to minor axis of the oval cross-section B--B is therefore1.45, which corresponds to a deformation of 20%. The proportion of thelength 5 of the deformed segment 6 in relation to the total length 4 ofthe door reinforcement tube 1 here is 20% and can be greater than 25% ifdesired. The two areas 9, 10 adjacent to the deformed segment 6 have anunchanged circular cross-section, characterized by the cross sectionsA--A and C--C. The transitions 11, 12 from the deformed segment 6 to theundeformed segments 9, 10 are smoothly rounded, so that no notch effectsoccur which would significantly reduce the energy absorption capability.Within the car door of FIG. 1, the minor axis 21 of the reinforcementelement 1 can be aligned in the direction of the arrow 4', or inalignment with the top and bottom of the door.

The material used for the example is a commercially availablecarbon-manganese-titanium boron steel with the following composition inpercent by weight: C=0.19, Si=0.42, Mn=1.19, P=0.012, S=0.001, A1=0.049,Cu=0.2, Cr=0.3, Ni=0.03, Mo=0.01, Ti=0.054, B=0.0037 and N=0.0147, withthe rest being iron and the customary impurities. With regard to theenergy absorption capability, the requirement is at least 1900 Joule.The tube produced from this material by hot rolling was annealed afterrolling and quenched with water.

FIG. 3 is a graph which shows the force applied (Y-axis) over thedeflection (X-axis), whereby the end line 13 marks the deflection of 150mm specified by a test specification. The area beneath the curve is thedesired energy absorption capability. Curve 14 is the force-deflectioncurve of a tubular steel reinforcement element having a circularcross-section extending over the entire length with an outside diameterof 31.8 mm and a wall thickness of 2.3 mm. The area beneath the curvegives a value of 2628 Joule. For purposes of comparison, Curve 15 showsthe force-deflection curve of the tubular steel reinforcement element 1according to the invention, with a segment 6 which has an ovalcross-section B--B and extends over a length 5 of 250 mm. The energyabsorption capability in this case is 3288 Joule, which corresponds to a25% increase, which can be utilized for a corresponding reduction ofwall thickness, diameter and thus weight.

FIGS. 4 and 4a show portions of a longitudinal cross-section and acorresponding cross-section along line D--D of another embodiment,whereby the same reference numbers are used for the same parts. Thecentral region 6 of the tubular steel reinforcement element isreinforced by way of example with an outer sleeve 16, which is pushedover the original tube before the cold forming and which is held inplace, for example, by adhesives. Since the outer sleeve 16 can befabricated independently of the original tube, the wall thickness 17 canvary to achieve an optimum with regard to the resistance increase andthe weight of the reinforcement element.

FIGS. 5 and 5a show portions of a longitudinal cross-section and acorresponding cross-section along line E--E of another embodiment,whereby the same reference numbers are used for the same parts. Thecentral region 6, in contrast to the embodiment illustrated in FIG. 4,is not reinforced by an outer sleeve 16, but in an integrated manner bymeans of a thicker wall 18. In this embodiment, the thicker wall 18 canbe shifted radially outward, or likewise radially inward, or can beuniformly distributed outward and inward. Before the subsequent coldforming of the segment 6 with its reinforced wall thickness to producean oval or elliptical cross-section, the tubular steel reinforcementelement is first formed to achieve a thicker/thinner wall and is thenheat-treated. The size of the thickened wall 18 and the radial positionof the thicker portion can be optimized in terms of weight and thedesired section modulus.

In summary, one feature of the invention resides broadly in a tubularsteel reinforcement element having high strength, toughness andresilience as an impact absorption element for reinforcing the door of amotor vehicle, in particular of a passenger car that is characterized bythe fact that the tubular steel reinforcement element (1) has a segment(6) extending longitudinally which has a non-circular cross-section anda curved exterior contour, the longer axis of which is at least 20%longer than the shorter axis which is perpendicular to it.

Another feature of the invention resides broadly in a tubular steelreinforcement element that is characterized by the fact that the segment(6) extends over the entire length (4) of the tubular steelreinforcement element (1).

Yet another feature of the invention resides broadly in a tubular steelreinforcement element that is characterized by the fact that the segment(6) extends over a specified length (5) in the central region of thetubular steel reinforcement element (1).

A further feature of the invention resides broadly in a tubular steelreinforcement element that is characterized by the fact that thecross-section is designed as an ellipse.

A yet further feature of the invention resides broadly in a tubularsteel reinforcement element that is characterized by the fact that theratio of the major axis to the minor axis of the ellipse is at least1.25.

Yet another feature of the invention resides broadly in a tubular steelreinforcement element that is characterized by the fact that thecross-section is designed as an oval.

An additional feature of the invention resides broadly in a tubularsteel reinforcement element characterized by the fact that the length ofsegment (6) is at least 25% of the total length (4).

A yet additional feature of the invention resides broadly in a tubularsteel reinforcement element that is characterized by the fact that inthe center of the formed segment, the ratio of major to minor axis isthe greatest, and decreases to the value 1 at both ends.

A further additional feature of the invention resides broadly in atubular steel reinforcement element that is characterized by the factthat the segment (6) has a reinforcement which is connected as anexternal (16) and/or internal sleeve to the tubular steel reinforcementelement.

A yet further additional feature of the invention resides broadly in atubular steel reinforcement element that is characterized by the factthat the segment (6) has a reinforcement which as a slit outer and/orinner sleeve is connected to the tubular steel reinforcement element,whereby the slit (19) faces the inside of the motor vehicle.

Another further additional feature of the invention resides broadly in atubular steel reinforcement element that is characterized by the factthat the segment (6) has a thicker wall than the adjacent sections (9,10) and makes a rounded transition to these sections.

A yet another additional feature of the invention resides broadly in atubular steel reinforcement element that is characterized by the factthat the inside of the segment (6) is filled with a medium having a lowspecific gravity.

Another yet further feature of the invention resides broadly in aprocess for the manufacture of a tubular steel reinforcement elementhaving high strength, toughness and resilience in which an original tubeis hardened and then cut into lengths, the process being characterizedby the fact that after the hardening, a segment extending along thelength of the tubular steel reinforcement element is cold-pressed.

A still further feature of the invention resides broadly in a processfor the manufacture of a tubular steel reinforcement element having highstrength, toughness and resilience in which an original tube is hardenedand then cut into lengths, the process being characterized by the factthat after the hardening or cutting, a reinforcing metal sleeve ispushed onto or into the tubular steel reinforcement element, and thenthis thicker-walled region is cold-pressed.

A still further additional feature of the invention resides broadly in aprocess for the manufacture of a tubular steel reinforcement elementhaving high strength, toughness and resilience in which an original tubeis shape hardened and then cut into lengths, the process beingcharacterized by the fact that the tubular steel reinforcement elementis shaped by sections to a thicker/thinner wall, and the thicker-walledsegment is cold-pressed after hardening.

Another still further additional feature of the invention residesbroadly in a process characterized by the fact that the shaping isperformed without any support.

Yet another still further additional feature of the invention residesbroadly in a process characterized by the fact that the shaping isperformed in a steel die.

Still another yet further additional feature of the invention resides ina process that is characterized by the fact that the degree of shapingis at least 15%.

Art hereby incorporated as reference includes German Patents No. 37 28476 C1; No. 27 50 867 A1; No. 2,426,705; No. 1,962,279; 2,319,124; and1,959,988 and U.S. Pat. Nos. 3,263,387 to Simpson; 3,868,796, to Bush;3,938,288 to Roubinet, 3,964,208 to Renner, 4,017,117 to Eggert, Jr.,4,090,734 to Inami, et al., and 4,564,232 to Fujimori, et al.

All, or substantially all, of the components and methods of the variousembodiments may be used with at least one embodiment or all of theembodiments, if any, described herein.

All of the patents, patent applications, and publications recitedherein, if any, are hereby incorporated by reference as if set forth intheir entirety herein.

The details in the patents, patent applications, and publications may beconsidered to be incorporable, at applicant's option, into the claimsduring prosecution as further limitations in the claims to patentablydistinguish any amended claims from any applied prior art.

The invention as described hereinabove in the context of the preferredembodiments is not to be taken as limited to all of the provided detailsthereof, since modifications and variations thereof may be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A door for a motor vehicle, said doorcomprising:at least one reinforcement element disposed within the door;said at least one reinforcement element being disposed within the doorto provide protection against collisions to the door of the motorvehicle; said at least one reinforcement element having:a first end, asecond end, and a central portion disposed between the first end and thesecond end; a length from said first end to said second end; across-sectional area, the cross-sectional area defining a first axis anda second axis substantially perpendicular to the first axis; thecross-sectional area has a first dimension taken along the first axisand a second dimension taken along the second axis; the first dimensionof the central portion being greater than the second dimension of thecentral portion; the cross-sectional area of the central portion of saidreinforcement element defines an oval; a ratio between the firstdimension taken along the first axis and the second dimension takenalong the second axis is at least 1.25 in the central portion; the ratiois greatest in the central portion; the ratio decreases from the centralportion to the first end and from the central portion to the second end;and the ratio decreases to about 1 at the first end and the second end;said at least one reinforcement element comprises a tube;said tubehaving a peripheral wall, the peripheral wall having a thickness; saidcross-sectional area, said ratio, said length and said thickness beingconfigured to absorb impact energy of collisions to the door; and saidfirst dimension of said reinforcement element being disposed within saiddoor in a lateral direction to absorb the impact energy of collisions tothe door.
 2. The door for a motor vehicle according to claim 1, whereinthe central portion of said reinforcement element comprises at least 25%of the length of said reinforcement element.
 3. The door for a motorvehicle according to claim 2, wherein the wall of the reinforcement tubehas an exterior surface and an interior surface, and said reinforcementelement further includes:means for adding additional strength to atleast the central portion of said reinforcement element; said means foradding additional strength comprising at least one of:a thickening ofthe wall of the reinforcement element along at least the central portionof said reinforcement element; and a sleeve means fastened to at leastone of:the exterior surface of at least the central portion of saidreinforcement element; and the interior surface of at least the centralportion of said reinforcement element.
 4. The door for a motor vehicleaccording to claim 3, wherein said sleeve has a length, and said sleevehas a slit along the sleeve length.
 5. The door for a motor vehicleaccording to claim 1, wherein the motor vehicle has a front, a rear, atop and a bottom, and the door further comprises:a front edge for beingdisposed toward the front of the motor vehicle and a rear edge for beingdisposed toward the rear of the motor vehicle; a top portion for beingdisposed toward the top of the motor vehicle and a bottom portion forbeing disposed toward the bottom of the motor vehicle; and said at leastone reinforcement element being disposed in said door with the first endof said at least one reinforcement element disposed towards the frontedge of said door, the second end of said at least one reinforcementelement disposed towards the rear edge of said door, and the second axisof said at least one reinforcement element disposed substantially in adirection extending from the top of the vehicle door to the bottom ofthe vehicle door.
 6. The door according to claim 5, wherein:the centralportion of said reinforcement element has a length, the length of thecentral portion comprises at least 25% of the length of saidreinforcement element; the door has a length extending from the frontedge of the door to the rear edge of the door; and the length of thereinforcement element substantially comprises the length of the door. 7.The door according to claim 6, wherein said oval central portion of saidat least one reinforcement element comprises:a first wall part and asecond wall part, said second wall part being disposed spaced apart fromsaid first wall part and each of said first wall part and said secondwall part being substantially flat; a third wall part and a fourth wallpart, said third wall part being disposed spaced apart from said fourthwall part; each of said third wall part and said fourth wall part beingdisposed between and connecting said first wall part to said second wallpart; and said third wall part and said fourth wall part beingsubstantially semi-circular and curved outwardly away from each other.8. The door according to claim 7, wherein:said cross-sectional area,said ratio, said thickness and said length of said at least onereinforcement element being configured to absorb impact energy of atleast 1900 Joules; said wall thickness is 2.3 millimeters; said lengthof said reinforcement element is 864 millimeters; said length of thecentral portion is 250 millimeters; said first dimension is 37millimeters; and said second dimension is 25.4 millimeters.
 9. A tubularsteel reinforcement element for a motor vehicle door, said tubular steelreinforcement element having:a first end, a second end, and a centralportion disposed between the first end and the second end; a length; across-sectional area, the cross-sectional area defining a first axis anda second axis substantially perpendicular to the first axis; thecross-sectional area having a first dimension taken along the first axisand a second dimension taken along the second axis; the first dimensionof the central portion being greater than the second dimension of thecentral portion; the first dimension taken along the first axis of thecross-section of the central portion is at least 20% greater than thesecond dimension taken along the second axis of the cross-section of thecentral portion; a ratio between the first dimension and the seconddimension is greatest in the central portion; the ratio decreases fromthe central portion to the first end and from the central portion to thesecond end; the ratio decreases to about 1 at each of the first end andthe second end; said reinforcement element being disposed within a doorwith said first dimension of said reinforcement element disposed in alateral direction to absorb impact energy of collisions to the door; andsaid cross-sectional area, said ratio and said length being configuredto absorb an impact energy of collisions to the door of at least 1900Joules in said lateral direction along said first dimension.
 10. Thereinforcement element according to claim 9, wherein the cross-sectionalarea of the central portion defines an oval;the ratio between the firstdimension taken along the first axis of the central portion and thesecond dimension taken along the second axis of the central portion isat least 1.25; the central portion of said reinforcement elementcomprises at least 25% of the length of said reinforcement element; saidtubular reinforcement element having a peripheral wall, the peripheralwall having a thickness; and said cross-sectional area, said ratio, saidthickness and said length of said at least one reinforcement elementbeing configured to absorb impact energy of collisions to the door of atleast 1900 Joules.
 11. The reinforcement element according to claim 10,further including:a means for adding additional strength to at least thecentral portion of said reinforcement element; said means for addingadditional strength comprising at least one of:a thickening of a wall ofthe reinforcement element along at least the central portion of saidreinforcement element; and a sleeve means fastened to at least one of:anexterior surface of at least the central portion of said reinforcementelement; and an interior surface of at least the central portion of saidreinforcement element.
 12. The reinforcement element according to claim11, wherein said sleeve has a length, and said sleeve has a slit alongthe sleeve length.
 13. The reinforcement element according to claim 11,wherein at least a portion of said reinforcement element is filled witha substance which has a low specific gravity, said substance comprisingat least one member of the group consisting essentially of: foam andwood.
 14. The reinforcement tube according to claim 11, wherein saidratio of said first dimension to said second dimension is 1.45 in thecentral portion.
 15. The reinforcement element according to claim 14,wherein said central portion of said at least one reinforcement elementcomprises:a first wall part and a second wall part, said second wallpart being disposed spaced apart from said first wall part and each ofsaid first wall part and said second wall part being substantially flat;a third wall part and a fourth wall part, said third wall part beingdisposed spaced apart from said fourth wall part; each of said thirdwall part and said fourth wall part being disposed between andconnecting said first wall part to said second wall part; and said thirdwall part and said fourth wall part being substantially semi-circularand curved outwardly away from each other.
 16. A reinforcement elementfor reinforcing a motor vehicle door, said reinforcement element havinga first end, a second end, a central portion disposed between the firstend and the second end, and a length from the first end to the secondend, said reinforcement element comprising:a cross-sectional area, thecross-sectional area defining a first axis and a second axissubstantially perpendicular to the first axis; the cross-sectional areaof the first end, the second end and the central portion each have afirst dimension taken along the first axis and a second dimension takenalong the second axis; each of the first end, the second end and thecentral portion comprise a ratio of said first dimension to said seconddimension; the ratio of the first dimension to the second dimension isgreatest in the central portion, the ratio in the central portion beingsubstantially greater than 1; the ratio of the first dimension to thesecond dimension decreases from the central portion to each of the firstend and the second end; said reinforcement element being disposed withinthe door with said first dimension of said reinforcement elementdisposed in a lateral direction to absorb impact energy of collisions tothe door; and said cross-sectional area, said ratio and said lengthbeing configured to absorb impact energy of collisions to the door. 17.The reinforcement element according to claim 16, wherein:thecross-sectional area of the central portion defines an oval and theratio of the first dimension to the second dimension in the centralportion is greater than 1.2; the cross-sectional area of each of thefirst end and the second end essentially define a circle and the ratioof the first dimension to the second dimension in each of said first endand said second end is about 1; and the central portion comprises atleast 25% of the length of said reinforcement element.
 18. Thereinforcement element according to claim 17, wherein:the ratio of thefirst dimension to the second dimension in the central portion is atleast 1.25; said reinforcement element comprises a tube; said tubehaving a peripheral wall, the peripheral wall having a thickness; andsaid cross-sectional area, said ratio, said thickness and said lengthbeing configured to absorb the impact energy of collisions to the door.19. The reinforcement element according to claim 18, further includingmeans for adding additional strength to at least the central portion ofsaid reinforcement element, said means for adding additional strengthcomprising at least one of:a thickening of the wall of the reinforcementelement along at least the central portion of said reinforcementelement; and a sleeve means fastened to at least one of:an exteriorsurface of at least the central portion of said reinforcement element;and an interior surface of at least the central portion of saidreinforcement element.
 20. The reinforcement element according to claim19, wherein:the ratio of the first dimension to the second dimension inthe central portion is 1.45; said oval central portion of said at leastone reinforcement element comprises:a first wall part and a second wallpart, said second wall part being disposed spaced apart from said firstwall part and each of said first wall part and said second wall partbeing substantially flat; a third wall part and a fourth wall part, saidthird wall part being disposed spaced apart from said fourth wall part;each of said third wall part and said fourth wall part being disposedbetween and connecting said first wall part to said second wall part;and said third wall part and said fourth wall part being substantiallysemi-circular and curved outwardly away from each other.